The present disclosure relates, in general, to electronics, and more particularly, to circuits and method for providing power to electronic devices. Such circuits may use Synchronous Rectification (SR) circuits, in which an Alternating Current (AC) supply voltage is rectified using one or more switching devices, such as transistors, that are switched on and off synchronously with the AC supply voltage. The switching devices may be controlled by signals from an SR control circuit.
The SR control circuit may turn a switching device on and off in response to a voltage across the switching device or a current passing through the switching device. A first threshold, i.e., an on threshold, may be used when determining whether to turn the switching device on. A second threshold, i.e., an off threshold, may be used when determining whether to turn the switching device off. A third threshold, i.e., a conduction detection threshold (which may also be referred to as an SR off detection threshold), may be used to determine that the switching device is no longer conducting current.
Reactive components associated with the switching device, such as a lead frame inductance of the switching device, may cause ringing or spikes in the voltage or current sensed by the SR control circuit. Such ringing or spikes have the potential to cause a premature change in the state of the switching device. For example, when the switching device is turned on, a ringing in the voltage or current sensed by the SR control circuit by the switching device may result, which may cause the SR control circuit to turn the switching device off prematurely, resulting in a reduction in the efficiency of the SR circuit.
A stray inductance in the circuit, such as a lead frame inductance of the switching device, may have a voltage drop across it due to a change in a current flowing through the stray inductance. The voltage drop across the stray inductance may alter a voltage that is being sensed in order to control the switching device. This alteration to the sensed voltage may lead to undesirable behavior, such as a premature turning off of the switching device. Prematurely turning off the switching device may, among other effects, decrease the efficiency of the circuit.
Accordingly, it is desirable to have SR control circuit that is able to automatically mitigate the detrimental effect of reactive components, such as stray inductances, of an SR circuit.
Those skilled in the field of the present disclosure will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of the embodiments.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments. This avoids obscuring the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the disclosures herein. The details of well-known elements, structures, or processes that are necessary to practice the embodiments and that are well known to those of skill in the art may not be shown and should be assumed present unless otherwise indicated.